More work porting towards Bootstrap 3.

  * Added dialog theme "boostrap" and enabled it by default. Removed jQuery UI theme.
  * Ported 'image' and 'table' plugins to Bootstrap 3 styles.
  * Changed behaviour on a couple of buttons.
  * Some bug-fixes hither and thither.

Some buttons (headers, font sizes) are still without icons, as there are no equivalent icons in Font Awesome. Oh well.
Any bugs are intentional, I can assure you.